Variable displacement internal combustion engines provide improved fuel economy and torque on demand by operating on the principle of cylinder deactivation. During operating conditions that require high output torque, every cylinder of a variable displacement internal combustion engine is supplied with fuel and air. Alternately, during operating conditions at low speed, low load, and/or other inefficient conditions for a fully displaced internal combustion engine, cylinders may be deactivated to improve the fuel economy of a vehicle equipped with the variable displacement internal combustion engine. For example, in operating a vehicle equipped with an eight cylinder variable displacement internal combustion engine, fuel economy will be improved if only four cylinders of the internal combustion engine are operated during relatively low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an internal combustion engine must perform to pump air from the relatively low pressure of an intake manifold, across intake and exhaust valves, and out to the atmosphere. The deactivated cylinders will disallow airflow across their respective intake and exhaust valves, thereby reducing pumping losses by forcing the internal combustion engine to operate at a higher intake manifold pressure. Since the deactivated cylinders do not allow gas to flow, additional losses are avoided by operating the deactivated cylinders as “gas springs” due to the compression and decompression of the gases trapped within each deactivated cylinder.
It is known in the art of engine cylinder deactivation to provide switchable hydraulic lash adjusters operable to either actuate the valves of a deactivatable cylinder or to maintain the valves in a closed position through lost motion features of the hydraulic lash adjusters. This lost motion occurs when the hydraulic lash adjusters telescope within a body or sleeve thereby allowing the respective intake or exhaust valve to remain closed even while the camshaft is rotating. Similar mechanisms may be provided within a hydraulic valve lifter, which includes a hydraulic lash adjusting mechanism and so may be referred to broadly as a hydraulic lash adjuster. A mechanical latching device, such as a locking pin, responsive to hydraulic fluid pressure is typically provided within the hydraulic lash adjusters to enable lost motion.
Hydraulic lash adjusters are supplied with pressurized oil through a lash adjuster oil feed gallery or passage to annular feed grooves, which provide oil pressure to take up the lash in the valve train between the tip of intake and exhaust valves and their associated rocker arm or other-actuator, such as, for example a roller finger follower. Hydraulic lash adjusters that are configured to effect cylinder deactivation typically have an additional hydraulic port, which connects through feed passages with a valved pressurized oil supply, to communicate fluid to the locking pin. A solenoid-actuated hydraulic control valve may be used to selectively communicate oil pressure from a main source of pressurized oil to the locking pin via a feed passage to effect cylinder deactivation. Alternatively, the solenoid-actuated hydraulic control valve operates to exhaust oil pressure from the locking pin and feed passage.
The smooth operation of the locking pin may be influenced by oil pressure excursions or spikes within the lash adjuster oil feed passage. The locking pin typically requires a small amount of lash, such that the locking pin can freely shuttle between the lost motion and activated valve opening modes. To ensure an adequate amount of lash to enable movement of the locking pin, a predetermined force, typically from a spring member, is employed to oppose the forces imposed on the locking pin by the hydraulic lash adjuster. Additional components, such as variable camshaft phasers, are typically actuated via the same pressurized oil circuit that feeds the lash adjuster oil feed passage. The actuation of these additional components may cause short term high oil pressure excursions that are outside the expected average range within the lash adjuster oil feed passage. This high oil pressure excursion may cause what is typically termed “lifter pump-up”, wherein the higher than expected oil pressure within the lash adjuster oil feed passage urges the hydraulic lash adjuster to overcome the force of the spring bias thereby eliminating the lash required to enable smooth operation of the locking pin.